Soft seat valves are relatively insensitive to contamination and leakage. Therefore, they are the most frequently used valves in hydraulic systems. The valve has a metallic valve core and a soft rubber seat (or insert). The soft rubber is molded in a cavity in the face of the valve core. Prior to molding a bonding agent is applied to the cavity. The quality of the bond is reduced if air is entrapped during the molding process or if the bonding agent is washed out during the process. Either defect causes voids in the seal between the valve core and the soft rubber. This leads to localized stress and results in premature valve failure.
A flat face on the soft rubber seating against a flat metallic surface on the valve housing has not been successful since the design leads to considerable variation in the pressure at which the valve opens. Better control of the opening pressure is obtained by dishing the face of the soft rubber seal but the thin perimeter of the seal has a very short service life.